The invention relates to a method and an apparatus for verifying or testing test substrates, i.e. wafers and other electronic semiconductor components, in a prober under defined thermal conditions. Such a verifying apparatus, known to the person skilled in the art as a prober, has a housing having at least two housing sections, in one housing section of which, designated hereinafter as test chamber, the test substrate to be verified is held by a chuck and is set to a defined temperature, and in the other housing section of which, designated hereinafter as probe chamber, probes are held. For verification purposes, the test substrate and the probes are positioned relative to one another by means of at least one positioning device and the probes subsequently make contact with the test substrate.
For particular test tasks, in particular for the measurement of very small currents, it is necessary to prevent interfering influences on the measuring arrangement which can corrupt the measurement results. Such an arrangement has for such tests a shielding system that can be used to minimize the electromagnetic influencing (EMI) of the measurement of the test substrates. A prober with electromagnetic shielding is known from DE 298 20 106 U1, which describes that an assembly for receiving the test substrates including the positioning unit thereof and also an assembly for receiving and positioning probes are shielded with a housing from the external electromagnetic influences. The cables to the control and evaluation units constitute the interfaces toward the outside. An optical and an electromagnetic shielding of the measuring equipment are thus obtained. A shielding with respect to low-frequency magnetic fields also proves to be particularly problematic. Such a low-frequency shielding can be obtained by means of thick-walled housings composed of ferromagnetic materials. However, accesses to such walls cannot be realized without significantly weakening the shield.
The problem of such housings is, however, the accessibility to individual components, in particular to the positioning units of the probes and/or the mount of the test substrate, generally designated as chuck. In U.S. Pat. No. 6,492,822 B2, therefore, parts of both positioning units are lead through the housing wall toward the outside, such that the manipulation thereof is possible from the outside without opening the housing. Such housing entrances prove to be disadvantageous, however, since they constitute an interruption of the shield.
DE 10 2007 053 862 A1 discloses a prober, the housing of which is subdivided in such a way that both the chuck with its chuck positioning unit and the probe mounts with the positioning units thereof are integrated in the shielding housing. The integration of such or comparable apparatuses and the cables thereof into the electromagnetic shielding system is effected in such a way that mutual influencing of the apparatuses and of the test substrate can be minimized even within the system. Despite the complex and variable shielding system, the individual components to be operated during a measurement cycle, such as e.g. the positioning unit of the chuck and also, if appropriate, of the probes, are accessible and observation of the test substrate during the measurement is possible. By way of example, the probe mounts are accessible by individual housing sections being open, while the housing section that directly surrounds the test substrate remains closed.
The configuration of the housing with a plurality of housing sections to be opened individually and the thus possible good accessibility of individual components of the prober with minimized interruption of the shield also allows the inclusion of an apparatus for signal conditioning, e.g. for signal preprocessing or for signal processing, into the electromagnetic shielding of the housing. Therefore, e.g. such cables which act as an antenna outside the housing and can corrupt the measurement can also be integrated into the shield of the housing. The prober proposed in DE 10 2007 053 862 A1 also encompasses the possibility of configuring the shielding system for shielding against low-frequency magnetic fields. Such shielding is obtained by means of housings or housing sections composed of thick-walled, ferromagnetic materials.
In the prober, a test substrate is arranged on the chuck and moved by means of the positioning unit of the chuck, generally also designated as chuck drive, in the working region, such that it is positioned relative to the probes of the prober. The test substrate is generally positioned in the horizontal, i.e. X Y, plane by means of a compound table and also by means of an apparatus for angular orientation and by means of a vertical, i.e. Z, advancing drive, which enables e.g. a feed movement of the test substrate in the direction of the probes arranged above the test substrate. By means of the positioning units of the probes, also designated as probe heads, a plurality of probes can be moved relative to one another or to a preferred direction of the test substrate in the X, Y and Z directions or in a feed movement to the test substrate. In alternative configurations, the probes are fixedly mounted.
For verification purposes, the probes, having the form of contact-making needles, make contact with the test substrate and verification signals are applied to or tapped off from said test substrate. The probes including the probe heads are generally situated outside the working region on a plate which upwardly delimits the working region and which often also serves for the mounting of the probes and in this case is designated as a probe mounting plate. The tips of the probes make contact with the test substrate through an opening in the plate, in which case, in order to optimize the electromagnetic shielding, the opening itself is made as small as possible or is supplemented by an electromagnetic shield, which is arranged above the test substrate and below the plate and has the necessarily small opening for the probes to reach through.
In probers, electronic components are verified with regard to their functional reliability preferably under the ambient conditions which correspond to the use conditions of the respective component, wherein the setting of the test substrate to defined temperatures usually in the range up to a few hundred degrees Celsius constitutes a main emphasis. The temperature of the test substrate is set by means of the chuck, which can be heated or cooled by means of suitable apparatuses.
It has been found however, that, via the plate that upwardly delimits the working region, and in particular via the opening therein and likewise via the contact of the probes with the test substrate, a heat exchange takes place between the working space and the overlying housing section, in which the probe mounts, the probe heads and also, if appropriate, the apparatus for signal conditioning are arranged and which shall be designated hereinafter as probe chamber.
Particularly in the case of relatively large temperature differences with respect to the ambient temperature, e.g. in the case of measurement temperatures of a few hundred degrees Celsius, all components and apparatuses arranged in the probe chamber are heated to such a temperature, which prevent, or at least make more difficult, exact positioning of the probes or maintenance of the position thereof over a relatively long verification period. This is because heating or cooling of the probe heads and also of the probes leads to drift phenomena on account of thermal expansion in the course of the measurement, these effects being intensified with the length of the verification tips. If the apparatuses for signal conditioning are arranged in a probe chamber, their electrical parameters are also altered and the measurement is corrupted. Furthermore, the housing of a probe chamber can also heat up to such a great extent that combustion can occur upon contact with the housing.
In order to overcome these problems, a prober is specified in which, in a housing section which lies outside the working region and encompasses at least one probe and the probe mount thereof, a temperature that is independent of the temperature of the test substrate is set by means of a temperature-regulated gas flow that flows through this housing section. The independent temperature setting of test substrate and probes makes it possible, in a manner dependent e.g. on the test temperature, on the thermal properties of the probes and/or on the type of test, to set the probes to such a temperature which either minimally influences the test substrate, maintains the positioning of the probes even for long-term tests, and/or to ensure the constant function of sensitive further components of the prober which are connected to the probes. Thus, e.g. even at very high or low test temperatures, the probes and the surroundings thereof such as e.g. signal conditioning apparatuses in the probe chamber can be set to the ambient temperature of the prober. It is nevertheless possible to maintain the temperature of the test substrate by means of suitable further measures described below.
The invention will be explained in greater detail below on the basis of an exemplary embodiment.